A water pigment inkjet ink has less bleeding, high image density and less coming out from the back when printed on a plain paper.
However, when a picture or a drawing needing much ink when printed on a plain paper is printed thereon, the plain paper is likely to curl back (the paper warps toward the opposite side of a printed side) right after printed.
When the plain paper curls back right after printed, papers are not smoothly fed in an inkjet printer. Particularly when a paper curls back in high-speed printing or both side printing, the paper is very difficult to feed.
Therefore, an inkjet ink causing a paper to curl back less even when printing a picture or a drawing needing much ink is demanded.
Particularly, a high-speed inkjet printer including a line head needs such an ink more than a serial printer.
As a conventional method of preventing the curl, Japanese published unexamined application No. JP-2004-136458-A discloses a method of applying an alcohol liquid to a paper, drying the paper at a recording position, and recording with an ink. Japanese published unexamined application No. JP-2008-18711-A discloses a recording method of discharging an ink and a reaction liquid reacting with the ink.
Japanese published unexamined application No. JP-2009-52018-A discloses an inkjet ink composition including diglycerin or polyglycerin and polyethyleneglycolmonoalkylether. Japanese published unexamined application No. JP-2009-287014-A discloses an inkjet ink composition including polyethyleneglycolmonomethylether.
The method disclosed in Japanese published unexamined application No. JP-2004-136458-A does not have an effect of preventing curl right after printed when a water ink is used in a large amount at high speed. The method disclosed in Japanese published unexamined application No. JP-2008-18711-A makes a recorder complicated and uneconomically discharges the reaction liquid in the same amount of the ink to prevent curl. Further, when a solid image is printed, both sides of a paper include much water content and the paper loses stiffness, which is difficult to feed. The methods disclosed in Japanese published unexamined applications Nos. JP-2009-52018-A and JP-2009-287014-A do not have an effect of preventing curl right after printed when a water ink is used in a large amount at high speed. Further, solvents included do not include sufficient average water content, resulting in unstable dischargeability.
Further, the conventional methods have the following problems (a) to (c).
(a) Solid image beading (dots adjacent to each other attracts each other, resulting in a rash on an image) or color bleed among colors occurs.
(b) When conventional multivalent metallic salts are used as a pretreatment liquid, an ink is difficult to fix.
(c) An inkjet ink (aqueous ink) causes cockling (a solid image waves) or curling back right after a solid image is printed.
Because of these reasons, a need exist for an image forming method capable of recording high-quality full-color images not only on plain papers but also on commercial printing papers at high speed and reducing curling right after printed, and further causing almost no beading of a solid image or color bleed among colors.